The present invention relates to high efficiency air filters and, more specifically, to methods of fabricating air filter assemblies to obtain an impermeable seal between the media and the surrounding frame.
In certain enclosed spaces it is essential that the air be completely free of any solid contaminants whatsoever, down to the sub-micron range. In order to insure that the required level of purity is maintained, it is the usual practise to install filters of the so-called "Absolute" type through which all air entering the enclosed space must pass. While filter media which will remove from air passing therethrough all particles down to the required size is readily available, it is difficult and costly to provide a completely air-tight seal around the entire periphery of the media where it meets the supporting frame.
In filters of the type with which the present invention is concerned, the filter core comprises an extended sheet of filter media formed into a series of zig-zag pleats with a corrugated spacer between the opposing walls of each of the pleats. This filter core is supported in a box-like frame, usually of plywood, but also in some constructions of heavy cardboard or sheet metal. The entire media edge, both ends and the continuous pleat edges, must be continuously sealed to the frame to avoid bypass. While sealing the media ends to the side frame members presents no great problem since an area of planar, surface-to-surface contact is available for such attachment, the deep (e.g., 12 inches) pleats have sinuous edges of considerable total length that require continuous, air-tight sealing to the adjacent surface of the frame. Thus, sealing the edges to the top and bottom frame members is considerably more difficult since there is essentially only line contact between the pleat edges and opposing frame surfaces.
One means for effecting the required sealing between media and frame which is currently in commercial use is that disclosed in U.S. Pat. No. 3,581,479 of Roger T. Goulet, issued June 1, 1971, and assigned to applicant's assignee. This involves forming a groove or channel across the inner faces of the top and bottom frame members for insertion of an elongated nozzle through which a liquid adhesive is injected as the nozzle is withdrawn from the groove. The amount of adhesive injected is sufficient to fill the groove and flow across the entire surface of the frame member to form a continuous bond, upon hardening, with the opposing pleated edges of the media. While filters constructed in this manner are satisfactory in operation, a degree of skill and care must be exercised in applying the adhesive as the nozzle is withdrawn from the groove in order to insure that a complete bond is achieved. Thus, fabrication in this manner requires trained individuals and is subject to operator error. Also, the effectiveness of the seal is dependent upon the flow characteristics of the adhesive and positioning of the assembly as the adhesive is applied and before it hardens.
It is a principal object of the present invention to provide a method of fabricating filter assemblies of the type discussed above which reliably forms a complete bond between filter media and frame in a manner more economical and simple than those previously used.
A further object is to provide a method of attaching a filter media edge to the opposite surface of a frame member wherein a liquid adhesive is applied to the frame member surface, and may therefore be visually observed for completeness and uniformity of coverage, prior to contact therewith of the media edge.
Other objects will in part be obvious and will in part appear hereinafter.